JP2007-334898 (A1) discloses a data delivery system including a reception section that receives request information having identification data of a plurality of clients from the clients in a predetermined period, a testing section that identifies the plurality of clients by using the identification data, an alarm section that generates an alarm signal about the clients that have not dispatched the request information in the predetermined period, a generation section that generates response data for an arbitrary one of the clients that is identified by the testing section, and a transmission section that transmits the response data to the arbitrary client.